A soundproofing assembly operates by “sound absorption” (in the field of middle and high frequencies) when the energy from the sound waves dissipates in an absorptive material.
Known from WO 2007/006950 is a soundproofing assembly of the aforementioned type, which comprises a base spring layer arranged on an inner surface of the automobile, and a layer of airtight heavy mass, to ensure, combined with the base spring layer, good sound insulation, through a “mass-spring” type of effect.
The soundproofing assembly described in WO 2007/006950 also comprises, above the heavy mass layer, at least one upper layer of absorbing foam that ensures good sound absorption.
Such an assembly therefore makes it possible to combine good sound insulation properties and significant sound absorption over a wide range of frequencies, while offering a substantial weight reduction relative to a traditional system of the simple “mass-spring” type.
The soundproofing assemblies described in WO 2007/006950 can satisfactorily be produced industrially, while keeping good acoustic properties, with a heavy mass layer having a minimum basis weight of about 2 kg/m2.
However, given the current constraints relative to reducing the mass of automobiles, automobile builders require that soundproofing assemblies be still further lightened.